World Anti-Doping Agency president Craig Reedie says he has received a letter from RUSADA that could break the deadlock preventing the Russian anti-doping agency from being formally reinstated.
WADA declared the Russian agency non-compliant with its rules in November 2015, when a WADA-funded investigation first confirmed the extent of Russia's systemic doping.
A 'roadmap to compliance' for RUSADA was later agreed between WADA and the Russian authorities and nearly all of its terms have now been met. There are, however, two sticking points and there has been no meaningful progress on them.
The Russian authorities have repeatedly refused to publicly accept the verdict of a second, much wider, WADA-funded investigation into Russia's cheating - the 2016 report prepared by Canadian law professor Richard McLaren.
They have also not given WADA, or any other international body, access to the data or samples still held at Russia's main anti-doping laboratory in Moscow.
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Of these matters, the first appears to be the most problematic for the Russians as it would mean them acknowledging their cheating was state-sponsored and effectively run by the sports ministry - not something they have shown any willingness to do, particularly in the build-up to next month's FIFA World Cup.
Despite this, WADA, in line with the International Association of Athletics Federations and the International Paralympic Committee, is determined to hold Russia to the roadmap commitments it made. But it is becoming increasingly clear that the global anti-doping body is under enormous pressure from the International Olympic Committee (IOC), which provides half of its budget, to compromise.
The other half of WADA's budget comes from national governments and the tension between their desire to hold Russia to account and the IOC's apparent desire to forgive and forget dominated a meeting in Montreal this week.
Speaking at the meeting in Montreal, Reedie said he has recently received word from Moscow that could solve the impasse.
"I hope it is a game-changer," Reedie told the insidethegames website.
"We've been exchanging correspondence now for the best part of a year and a half and there have been very many differentiations of the words, this one is probably the most encouraging one that we have had.
"My first look at it is that they are getting closer to acknowledging that there was an error.
"Someone said to me it is only semantics but semantics matter in this game - they matter in Moscow and they matter within this organisation and let's hope I am right."
The letter will now be reviewed by WADA's independent compliance review committee at its next meeting in June.
